George b



(N o Model.) G. B. N. DOW.

- SCREW.

N0. 366,158. Patented July 5., 1887.

WWW-c0009 H gave mm my 0% 1am. I /Q4/fiw N. PETERS. Phnm-Lithognp ur.wan; n n nnn UNiTED STATES GEORGE B. N. DOlV, OF MANCHESTER, NEYVHAMPSHIRE, ASSIGNOR TO CHARLES H. I-IUTOHINSON AND BRADBURY P. OILLEY,BOTH OF SAME PLACE.

SCREW.

SPECIFICATION forming part of Letters Patent No. 366,158, dated July 5,1887.

Application filed March 18, 1856.

To (LZZ whom it may concern:

Be it known that I, GEORGE E. N. Dow, a citizen of the United States,residing at Manchester, in the county of I-Iillsborough and State of NewHampshire, have invented certain new and useful Improvements in Screws;and I do declare the following to be a full, clear, and exactdescription of the invention, such as will enable others skilled in theart to which it appertains to make and use the same, reference being hadto the accompanying drawings, and to the letters and figures ofreference marked thereon, which form a part of this specification.

This invention relates to an improvement in screws; and it consists inconstructing the head of a screw with a countersunk depression,which isprovided with a longitudinallycurved slot for the reception of the bitof the driver; and it further consists in certain peculiarities of theconstruction, as will be hereinafter set forth.

In the annexed drawings,illustrating my invention, Figure 1 is aperspective of my improved screw. Fig. 2 is a top plan View. Fig. 3 is asection showing the curvature of the slot for the driver; and Fig. 4. isa top plan of the head, showing two slots at right angles.

Like letters of reference indicate like parts in all the figures. V

In a screw patterned after my improved form the concaved depression inthe head starts from near the outer periphery and slopes down to nearthe bottom of the head, stopping at a sufficient distance from thebottom of the head to prevent a weakening of the screw-head, which mighttake place through the removal of the metal when too deeply hollowedout. However, this countersunk depression maybe deeper or shallower, asdesired, for in constructing the screw-head said head may be made largerthan that of the ordinary screw, and thus an opportunity for a deeperconcave be afforded. Diametrically across the head, through thecountersunk depression and extending below the same, as shown in Fig. 3,is cut a slot for the reception of the driver, said slot being generallycurved longitudinally or along its lower surface from end to end, thusat an angle with said line.

Serial No. 195.6351. (No model.)

making it of approximately an equal depth throughout. The slot ispreferably so 1) roportioned to the depression that a chord drawn fromend to end ofthe bottom are of the slot will pass through the lowermostpoint in the countersunk depression. \kVhen this is the case,it isobvious that the terminal portions of the slot will have no bottom ifthe head is conical externally.

Some of the advantages to be derived from the use of my improved screware as follows: When the bit of the driveris inserted into the slot, itworks toward the center, and is not liable to slip out,whcther thedriver is held in an upright or an oblique position-i. c.,wheth er thedriver is held in line with thescrew-shaft or Further, it is possible toturn the screw with the driver held down at nearly a right angle withthe axial line ofthe screw, the bit having the same purchase andfirmness as when held in an upright positiona result which isunattainable with the common screw and its driver; hence the screw mayin this. manner be driven in places where otherwise it could not.

It will also be observed that the weight of the driver will keep it inplace in the slot, for it cannot slip out by moving laterally, themiddle portion of the slot being lower than the rest, and therefore inorder to. get out it must ride up an inclined or curved surface, andthis will not likely occur if the driver is properly handled; whereas ifthe slot were straight across the bottom the driver might easily passout of it without any negligence on the part of the operator. It is notthen nec essary to press upon the driver in order to keep it in place inthe slot, and injury to the thread of the screw or to the substance intowhich it is inserted is obviated.

In the ease of ordinary screws there is a great liability of their beingturned or deflected from the true course that the operator designs themto pursue by the uneven pressure of the driver,which at one time will bepressing with greatest force on one side of the center of the screw-headand. at another time on the other. By my improvement this difficulty isavoided, as the pressure is kept always upon the center of the headdirectly in line with the center of the screw-shaft, and consequentlydirectly over the point ofthe screw, and this constant central pressurewill be maintained, although the driver is turned to the right orleft.This renders the screw as well as the driver more secure from breakage.Perhaps, however, the greatest benefit arising from the use ofmyimproved screw is the facility with which the bit of the driver willfind the slot in the head, for if it is not inserted therein at thefirst movement of the driver a turn in one direction or the other willsurely bring it into the slot, ready for work. Thus time will be saved,for more screws can be driven in a given time, and consequently morework done.

The concave-headed screw will in many cases obviate the necessity ofplugging, for the putty or other substance used can be inserted and heldwithin the cavity and its slot, thus leaving the outer surface smooth,or capable of being made so. In plugging the heads of common screws invery nice work it has been found that more or less glue is leftunavoidably between the plug and the screw-head, and this glue, acted onby the weather or by other influences, will swell and force out theplug, thereby marring and defacing the surface of the work. Thecountersunk head avoids this diificulty, for an air-space is leftbetween the plug and the bottom of the cavity in the head, into whichspace this glue is received, and consequently room is afforded for it toswell without disturbing the plug.

Thus far I have spoken of the screw-head as being provided with a singleslot. It is obvious, however, that it may have more than one slot. belocated at right angles to the first, and in certain cases it maybedesirable to have even A second similarly-formed slot'may' the axis ofthe screw; but there are many situations where, in addition to thedisadvantage of having the screw-head close to an object above, there isthe additional disadvantage of having but a limited range of movementfor the handle of the driver, said movement being insufficient to give acomplete revolution to the screw. In this case more than one slot isnecessary, for when the screw has been partially rotated as far as themovement of the driver will allow the latter can be taken out and putinto the slot, the rotation of the screw continued, and so on.

Having thus described my invention, what I claim as new, and desire tosecure by Letters Patent, is-

1. As a new article of manufacture, ascrew having a countersunk head anda transverse parallel-sided slot for the reception of the driver, asdescribed.

2. As anew article of manufacture, a screw provided with a concaved headand a longitudinally-curved slot situated diametrically across saidconcaved head, substantially as described.

. Intestimony whereoflaffix my signaturein presence of two witnesses.

GEORGE B. N. DOW.

Witnesses:

JOHN G. BIOKFORD, JOHN A.'RIDDLE.

